I ran with that exact size combination (120-70/17 & 160-80/15) for a little over a year. See post for reference:
www.hdstreetforums.com
The combination did take some getting used to, turning in was quicker than stock and it did take a month or so to get used to. Other than that, no issues. I originally changed to eliminate exhaust scraping and it worked as intended. Note that I also changed from stock suspension to heavy duty progressives in the rear to prevent potential rubbing.
New Meat
Decided to get some new tires for my street, already mounted the front (Shinko 016 Verge 2x) and should get around to the rear (Shinko 777) sometime this week. new sizes are: front: 120/70-17 rear: 160/80-15 a little beefier especially in the back :) should be fun.
The combination did take some getting used to, turning in was quicker than stock and it did take a month or so to get used to. Other than that, no issues. I originally changed to eliminate exhaust scraping and it worked as intended. Note that I also changed from stock suspension to heavy duty progressives in the rear to prevent potential rubbing.